1. Field of the Invention
The present invention relates to a white balance adjusting device for use in a camera in which the image of a field to be photographed is picked up and then a video signal representing the field is created.
2. Description of the Related Art
Recently, there has been developed an attractive electronic still camera system wherein an image pickup device, such as a solid image pickup element, an image pickup tube or the like, is combined with a recording device employing, as a recording medium, an inexpensive magnetic disc having a comparatively higher memory capacity for photographing an object electronically recording the object into the rotating magnetic disc and reproducing an image by a television system or a printer separately provided.
In the above-mentioned electronic still cameras, there is included an electronic still camera which is provided with a photographic mode including a still mode wherein an image of a field is picked up and is then recorded as a still image and a movie mode wherein the camera can photograph a field as a movie camera by connecting a video adapter to the camera. In this type of electronic still camera, to record a color image, the white balance of the camera must be adjusted in accordance with the kinds of illumination lights in photographing, according to or regardless of whether the photographic mode is the still mode or movie mode.
Because a color camera cannot adapt itself to colors like human eyes do, the color camera must be adjusted such that even in a television receiver the black and white colors of the field can be seen as black and white as they actually are. For this reason, in order to make the color separation components of a video signal obtained from an image pickup device uniform according to the color temperatures of the illumination lights, the camera white balance adjustment is performed to thereby adjust the amplification gains thereof.
In general, a movie camera (video camera) is set to have a property of a comparatively slow response from the input of the color temperature data of the field by the color temperature detection device thereof to the execution of the white balance adjustment. This slow response results because the color temperatures in the natural world vary in a wide range of time but the variations thereof are normally slow.
In other words, in the movie camera, because great importance is placed on the correlation (continuity) of the screen thereof, the response property for the white balance adjustment is set slow.
On the other hand, when the electronic still camera is set in the still mode for photographing, a shutter chance occurs in an instant and thus the white balance adjustment must be carried out in accordance with the color temperature of the field in that instant. For example, such a case may occur in which, after the camera is directed toward a room, the camera is directed in an instant outside of the room for photographing.
By the way, the still mode of the electronic still camera includes a single photographic mode and a sequential photographic mode. The single photographic mode is a basic operation mode in which when a shutter release is executed, the image of the field is picked up by a frame and a video signal representing the still image thereof is recorded.
On the other hand, the sequential photographic mode is an operation mode in which, while the shutter release is being executed, the image of the field is picked up sequentially every given period of the time and a video signal representing the still image thereof is recorded.
In the single photographic mode, as discussed above, the white balance adjustment must be made in compliance with the color temperature of the field in the instant of the shutter release, but this cannot apply to the sequential photographic mode. That is, due to the fact that the reflected light of the field (object) is detected by a color temperature sensor and the white balance adjustment is made by a control part according to the detected output of the sensor, when the sequential photographic mode is used to photograph, for example, a moving object, if the background of the object is varying in succession, then the white balance adjustment must be made according to the variations of the color temperature of the varying background.
As a result of this, the image of the object is tinged with the color of the background, which damages the homogeneity (which means that the object is photographed substantially in the same color hue) of the same main object in a plurality of still images picked up by means of the sequential photographic mode.
In the sequential photographic mode, as in the movie mode, due to the high correlation between a series of images photographed, the homogeneity of the main object is required.